Broadcast television production and transmission often involves simultaneous display of the video content of multiple video streams, to allow people to see what is in each stream. This might be images from the different cameras and other video sources in a studio during the production process, or the many channels being processed for transmission in a playout facility. Historically, with analogue television signals, this monitoring was achieved with a ‘wall’ of multiple small display devices (‘monitors’) each showing the image content of a single video stream. These would be used for basic content monitoring: allowing a check of what each camera is pointing at, or whether the playout device for each channel is operating correctly. A small number of larger monitors would be provided for more stringent quality checks and to aid creative decision making. The signals to the monitors would typically be connected through a crosspoint switch, also known as a router, allowing any signal source to be connected to any monitor.
This approach can also be used with television signals digitised as continuous streams of data, such as the ‘SDI’ signals widely used in current television production and playout systems.
Multiviewers enable different video streams from a large number of different sources to be brought together and viewed at a common viewing location, typically in real time. Such systems find application in closed circuit television-based security (in which feeds from a large number of cameras need to be viewed simultaneously) but are particularly useful in a broadcasting environment in which there is a requirement that somebody can monitor a large number of video sources simultaneously. To that end, it is known to put a number of videos on a single screen which is, in effect, sub-divided into separate windows, each displaying a respective video stream. This approach is becoming more popular and useful with the increasing availability of large display screens.
A multiviewer typically combines a number of video inputs to prepare a composite video output. A difficulty in constructing a multiviewer is that a large number of video signals need to be connected to it, and these require a large amount of bandwidth. Current devices have a limit to the number of input video streams and output TV screens that they can therefore handle. Additionally or alternatively, these transmission requirements can place constraints on the location of the multiviewer relative to the sources of the video streams.